The campaign arm of the House GOP is targeting Vice President Kamala Harris in an ad that calls her the “enabler in chief,” elevating the No. 2 as Democrats consider whether to dump President Biden from the ticket. Over ominous music, the 75-second clip shows Ms. Harris talking about how proud she’s been to serve alongside Mr. Biden. It also says she struggled to tackle illegal immigration — one of many tasks delegated to her early in Mr. Biden’s term. The National Republican...